Conventionally, films composed of a polyvinylidene chloride or vinylidene chloride copolymer (hereinafter abbreviated as PVDC) are known as a film with excellent oxygen gas barrier properties.
However, PVDC generates toxic gas with combustion.
Therefore, films composed of polyvinyl alcohol and an ethylene-vinyl alcohol copolymer are known. However, these films are disadvantageous in that they have poor gas barrier properties under high humidity.
Furthermore, a vapor deposition film in which inorganic oxide is vapor deposited on the film is known as well, but the film is disadvantageous in that it is low in flexibility, and may cause reduction in gas barrier properties with cracks created in secondary operation.
Thus, there has been examined development of a film with excellent gas barrier properties even under high humidity, to be specific, a composite film with gas barrier properties produced as the following has been proposed: for example, a diisocyanate component is allowed to react with a diol component containing C2 to 8 alkylglycol to produce polyurethane resin with gas barrier properties, and a layer including the polyurethane resin and a substrate film layer are laminated. For the method for forming a composite film with gas barrier properties, Patent Document 1 has proposed a method in which water dispersion of polyurethane resin is applied on a substrate film and dried.